Study Of Organic Light Emitting Devices To Improve The Performance

Organic light emitting devices(OLEDs) have some advantages, such an active emitting, low cost, light weight, low power consumption, high luminance, high efficiency, operating within large temperature region, being able to achieve full color and flexible display, and so on. Since C. W. Tang reported OLEDs with high luminance and low operating voltage, the OLEDs as a new technology for planar display were paid much attention to by academia and industry.In this paper, we introduced our work as follows: Firstly, because the OLEDs have some disadvantages, such as, low efficiency and high turn-on voltage, and so on. The turn-on voltage is a key parameter to describe the performance of the devices. In order to apply the OLEDs in practice, we must low the turn-on voltage. At present, P-doped hole transport layer is used abroad to reduce the turn-on voltage of the OLEDs. The disadvantage of P-doped hole transport layer is the complex processing and the repeatability is bad. In our paper, we used multi-layer NPB/MoOx/NPB as hole transport layer to efficiently reduce the turn-on voltage of the device. The advantage of multi-layer NPB/MoOx/NPB for hole transport layer is easy process to fabricated the devices. The driving voltage of tris(8-hydroxyquinoline) aluminum (Alq3)-based organic light-emitting devices (OLEDs) could be lowered by 0.8V at 1000cd/m2 by using multiple structure of NPB/MoO3/NPB. Figure 1(a) and (b) shows the voltage-current density and voltage-luminance characteristics of the devices and figure 3 showed the normalized EL intensity of the devices(details are shown in the second chapter of our paper).The electrode consist of Ag(20 nm)/Alq(85 nm)/Ag(20 nm)/Alq(85 nm) and we obtained the same spectra, efficiency, and color coordinates for the both sides of the devices by adjusting the parameter of the electrodes. Figure 4 shows the structure of the semitransparent device. As can be seen, the cathode and anode have the same Fig.1(a) The voltage-current density Fig.1(b) The voltage-luminance curve of curve of device A, B, C, D, and E device A, B, C, D, and E Fig.2(a) The voltage-current density Fig.2(b) The voltage-luminance curve of device A,F,G,and H curve of device A, F, G, and H. Fig.3 The normalized EL intensity of devices A, F, G, and H. Fig.4 The structure of the semitransparent device structure except for the additional glass for the anode, which makes the very little difference for the spectra, luminance and efficiency between the two sides of the device.Figure 5 shows the normal spectra of the devices A and B. As can be seen, the device with two periods electrodes has stong microcavity effect. Device A have two resonant emission peaks and we also can see that the narrowness of the full width at half maximum of the DPVBi and (F-BT)2Ir(acac) emission in device A is observed. is observed. There is only a little difference between the sides of the device for the spectra. Figure 6a shows the spectra from the cathode side of the device A at different viewing degree. With increasing viewing angle, the peak wavelength shifts to a shorter wavelength due to the microcavity effect in the device. Figure 6b shows the spectra from the anode side of the device A at different viewing degree, which has the same trend to that of cathode side. Fig.5 The structure of the semitransparent device Fig.6a The structure of the semitransparent device Fig.6b The structure of the semitransparent deviceFinally, flexible display and light device with OLEDs technology is one of the very important applications. The currently used indium tin oxide (ITO) has significant shortcomings for low-cost, large-area, and flexible device applications that include rising cost of indium, brittleness, need for high growth temperature and special technology, and the diffusion nature of indium ions which is harmful to the long-term performance of OLEDs.Figure 7 shows the measured and calculated optical transmittance curves of multilayer MAM as a function of the wavelength in visible region. The measured optical transmittance curve of ITO was also plotted in Fig.1. It can be seen that a high average transmittance of over 84% is obtained for the MAM-based transparent multilayer, which is comparable with the conventional ITO. So we can fabricate the nonmicrocavity OLEDs with the MAM anode. The spectra of the white light OLEDs with MAM anode is shown in figure 8. Fig.7 The structure of the semitransparent device Fig.8 The structure of the semitransparent device...